Chapter 21 - Mortality & Morbidity

Question 1

Factors contributing to mortality & morbidity

Answer 1

Variation:
- by age and sex
- between geographical areas, e.g. countries, regions of a country, urban and rural areas
- by social class, e.g. manual and non-manual workers over time, e.g. mortality rates usually decrease over time

None of these categories provide a direct causal explanation of the observed differences. Rather they are proxies for the real factors which cause the observed differences. Such factors are:
- occupation
- nutrition
- housing
- climate / geography education
- genetics
- HIV status.

Question 2

Types of selection

Answer 2

Temporary initial selection
Each group is defined by a specified event (the select event) happening to all the members of the group at a particular age, e.g. buying a life assurance policy or retiring on ill-health grounds

Class selection
The population can be divided into classes, for example, gender with classes of male and female or occupation with classes of manual and non-manual employment. The stochastic models (life tables) are different for each class. There are no common features to the models, they are different for all ages.

Time selection
Within a population, mortality and morbidity normally varies with calendar time, essentially due to medical advances. This effect is usually observed at all ages. The usual pattern is for mortality rates to become lighter (improve) over time, although there can be exceptions, for example, due to the increasing effect of AIDS in some countries

Adverse selection
Adverse selection (or anti-selection) is characterised by the way in which the select groups are formed rather than by the characteristics of those groups. So, any of the previous forms of selection may also exhibit adverse selection. Adverse selection usually involves an element of self-selection, which acts to disrupt (act against) a controlled selection process which is being imposed on the lives. This adverse selection tends to reduce the effectiveness of the controlled selection.

Spurious selection
When homogeneous groups are formed, we usually assume that the factors used to define each group are the cause of the differences in mortality observed between the groups. However, there may be other differences in composition between the groups, and it is these differences that are the true cause of the observed mortality differences.Ascribing mortality differences to groups formed by factors which are not the true causes of these differences is termed spurious selection